Antennas are used in sensors, radars and radio communication systems to transmit and/or receive electromagnetic signals wirelessly at frequencies over which the antenna element(s) experience electromagnetic resonance. Resonant dipole antennas are a class of antennas where the electromagnetic radiation emissivity/sensitivity is pronounced at the antenna's fundamental frequency and harmonics of the fundamental frequency. Resonant dipoles have low to moderate gain, which is useful in transceiver systems that require general insensitivity to the relative direction (and/or orientation) of transmit and receive antennas, such as mobile communications. They also have relatively high efficiency at resonance, which is commonly represented as a low return loss. In general, a dipole antenna spanning a length (l) will exhibit its fundamental resonance frequency ffund (also known as the first harmonic) over electromagnetic emissions having wavelength(s) given by:2l≅λfund  (1)
TABLE 1Required Communications Frequency BandsCountryUMTSGSMEurope2100900United States/Canada850 or 1700 or 21001900 or 850 China2100900Japan2100(not supported)Argentina 8501900 Brazil21001800 Chile850 or 1900850 or 1900India2100900Egypt2100900South Africa2100900
As shown in FIG. 1, a 0.5 m long dipole antenna will have its fundamental frequency 1 close to 300 MHz and harmonic resonances 2A,2B at odd integer multiples (900 MHz and 1500 MHz) of the fundamental frequency 1. Although dipole antennas have some desirable characteristics for mobile device applications, such as low to moderate gain and high efficiency (low return loss), their conductive pass bands 1,2A,2B do not align with the allocated communication frequency bands (UMTS 1700, UMTS 1900, UMTS 2100, GPS, GSM 850, GSM 900, GSM 1700, GSM 1800, and WiFi) typically used by these devices. As a consequence, multiple antenna elements are required to cover the frequency spectrum requirements of a typical mobile communications device. Table 1 shows the required frequency bands for cellular communications using voice, text, and mobile data over Universal Mobile Telecommunications Systems (UMTS) third-generation (3G) systems in various countries around the world, as well as the required frequency bands for cellular communications using voice, text and mobile data over Global System for Mobile Communications (GSM) second-generation (2G) systems in those countries. Most countries recommend supporting a larger number of frequency bands than those shown in TABLE 1 depending upon the size of its geographic territory and/or telecommunications market. The larger number of frequency bands allows multiple carriers (service providers) to supply the national population and bid for premium (required) bands in regions where they have higher customer concentrations, while lowering carrier costs by using lower value (recommended) bands in regions where their customer concentration is less strong.
As a result of this general landscape within the industry, a single service provider will likely require mobile wireless devices that contain multiple antennas/radio systems to faultlessly navigate its domestic territory or provide global portability. The better broadband antennas will electrically communicate with 33% bandwidth (Δf/fcenter) and have a peak efficiency of 70-80%, where Δf=fupper−flower. These broadband antennas would allow a single antenna element to cover two bands that are closely positioned in frequency, such as the GSM 1700 and GSM 1800 bands (see TABLE 2), but not all the frequency bands at which the mobile wireless unit must communicate and certainly not at peak efficiency. Multiple antenna elements are undesirable since each element adds to the overall cost and occupied volume.
TABLE 2Select Frequencies of Cellular Communications BandsFrequency BandUplink (MHz)Downlink (MHz)UMTS21001920-19802110-217019001850-19101930-1990  1700 IX1749.9-1784.91844.9-1879.9 1700 X1710-17702110-2170GSM19001850.2-1910.21930.2-1990.218001710.2-1785.81805.2-1879.8 900880-915925-960 850824-849869-894
Filtering components are electrically coupled with the antenna system in the RF front-end to isolate specific frequency bands of interest for a given transceiver (radio/radar) application. The filtering components prevent electromagnetic emissions that fall outside of the desired frequency range(s) from interfering with the signal(s) of interest and are generally required to isolate the chosen frequency band from any undesirable frequency emissions to a level −40 dB or more in most applications. As shown in TABLE 2, mobile communications system designate a portion (subband) of the communications band for uplink frequencies (from the mobile device to the tower) and another portion for downlink frequencies (from the tower to the mobile device). The RF front-end must fully isolate these distinct signaling frequencies from one another and operate simultaneously if full duplex mode communications is desired. Acoustic-wave filters are generally used in cellular communications systems to isolate uplink frequencies 3 from downlink frequencies 4 and provide the requisite better than −40 dB signal isolation as shown in FIGS. 2A&2B. In addition to adding cost to and occupying space on the mobile platform, acoustic-wave filters will contribute 1.5 dB to 3 dB insertion loss between the antenna and the send/receive circuitry. Higher insertion losses are undesirable as they divert the available power to the radio and away from other useful functions.
Mobile wireless devices have radios with fixed frequency tuning, so a single radio system will only communicate over a specific frequency band. As a result of the fixed uplink/downlink tuning most mobile devices will have multiple radio systems since a given wireless carrier may not have license to operate at the premium (required) frequency bands shown in TABLE 1 throughout an entire nation. A given wireless service provider will be less likely to have access to the premium or required frequencies in foreign countries. The need for additional radios in their mobile systems is undesirable as it adds considerable cost to the service.
1. Description of the Prior Art
The following is a representative sampling of the prior art.
Kinezos et al., U.S. Ser. No. 12/437,448, (U.S. Pub. No. 2010/0283688 A1), “MULTIBAND FOLDED DIPOLE TRANSMISSION LINE ANTENNA”, filed May 7, 2009, published Nov. 11, 2010 discloses a multiband folded dipole transmission line antenna including a plurality of concentric-like loops, wherein each loop comprises at least one transmission line element, and other antenna elements.
Tran, U.S. Ser. No. 12/404,175, (U.S. Pub. No. 2010/0231461 A1), “FREQUENCY SELECTIVE MULTI-BAND ANTENNA FOR WIRELESS COMMUNICATION DEVICES”, filed Mar. 13, 2009, published Sep. 16, 2010 discloses a modified monopole antenna electrically connected to multiple discrete antenna loading elements that are variably selectable through a switch to tune the antenna between operative frequency bands.
Walton et al., U.S. Pat. No. 7,576,696 B2, “MULTI-BAND ANTENNA”, filed Jul. 13, 2006, issued Aug. 18, 2009 discloses the use of multiple assemblies consisting of arrays of discrete antenna elements to form an antenna system that selectively filters electromagnetic bands.
Zhao et al., U.S. Ser. No. 12/116,224, (U.S. Pub. No. 2009/0278758 A1), “DIPOLE ANTENNA CAPABLE OF SUPPORTING MULTI-BAND COMMUNICATIONS”, filed May 7, 2008, published Nov. 12, 2009 discloses a multiband folded dipole structure containing two electrically interconnected radiating elements wherein one of the radiating elements has capacitor pads that couple with currents the other radiating element to produce the “slow-wave effect”.
Su et al., U.S. Ser. No. 11/825,891, (U.S. Pub. No. 2008/0007461 A1), “MULTI-BAND ANTENNA”, filed Jul. 10, 2007, published Jan. 10, 2008 discloses a U-shaped multiband antenna that has internal reactance consisting of a ceramic or multilayer ceramic substrate.
Rickenbrock, U.S. Ser. No. 11/704,157, (U.S. Pub. No. 2007/0188399 A1), “DIPOLE ANTENNA”, filed Feb. 8, 2007, published Aug. 16, 2007 discloses a selective frequency dipole antenna consisting of a radiator comprising conductor regions that have alternating shape (zig-zag or square meander lines) with an interleaving straight line conductor section, as well as a multiband antenna dipole antenna consisting of a plurality of radiators so constructed, which may be deployed with and without coupling to capacitive or inductive loads.
Loyet, U.S. Pat. No. 7,394,437 B1, “MULTI-RESONANT MICROSTRIP DIPOLE ANTENNAS”, filed Aug. 23, 2007, issued Jul. 1, 2008 discloses the use of multiple microstrip dipole antennas that resonate at multiple frequencies due to “a microstrip island” inserted within the antenna array.
Brachat et al., U.S. Pat. No. 7,432,873 B2, “MULTI-BAND PRINTED DIPOLE ANTENNA”, filed Aug. 7 2007, issued Oct. 7, 2008 disclose the use of a plurality of printed dipole antenna elements to selectively filter multiple frequency bands.
Brown and Rawnick, U.S. Pat. No. 7,173,577, “FREQUENCY SELECTIVE SURFACES AND PHASED ARRAY ANTENNAS USING FLUIDIC SURFACES”, filed Jan. 21, 2005, issued Feb. 6, 2007 discloses dynamically changing the composition of a fluidic dielectric contained within a substrate cavity to change the permittivity and/or permeability of the fluidic dielectric to selectively alter the frequency response of a phased array antenna on the substrate surface.
Gaucher et al., U.S. Pat. No. 7,053,844 B2, “INTEGRATED MULTIBAND ANTENNAS FOR COMPUTING DEVICES”, filed Mar. 5, 2004, issued May 30, 2006 discloses a multiband dipole antenna element that contains radiator branches.
Nagy, U.S. Ser. No. (U.S. Pub. No. 2005/0179614 A1), “DYNAMIC FREQUENCY SELECTIVE SURFACES”, filed Feb. 18, 2004, published Aug. 18, 2005 discloses the use of a microprocessor controlled adaptable frequency-selective surface that is responsive to operating characteristics of at least one antenna element, including a dipole antenna element.
Poilasne et al., U.S. Pat. No. 6,943,730 B2, “LOW-PROFILE, MULTI-FREQUENCY, MULTI-BAND, CAPACITIVELY LOADED MAGNETIC DIPOLE ANTENNA”, filed Apr. 25, 2002, issued Sep. 13, 2005 discloses the use of one or more capacitively loaded antenna elements wherein capacitive coupling between two parallel plates and the parallel plates and a ground plane and inductive coupling generated by loop currents circulating between the parallel plates and the ground plane is adjusted to cause the capacitively loaded antenna element to be resonant at a particular frequency band and multiple capacitively loaded antenna elements are added to make the antenna system receptive to multiple frequency bands.
Desclos et al., U.S. Pat. No. 6,717,551 B1, “LOW-PROFILE, MULTI-FREQUENCY, MULTI-BAND, MAGNETIC DIPOLE ANTENNA”, filed Nov. 12, 2002, issued Apr. 6, 2004, discloses the use of one or more U-shaped antenna elements wherein capacitive coupling within a U-shaped antenna element and inductive coupling between the U-shaped antenna element and a ground plane is adjusted to cause said U-shaped antenna element to be resonant at a particular frequency band and multiple U-shaped elements are added to make the antenna system receptive to multiple frequency bands.
Hung et al., U.S. Ser. No. 10/630,597 (U.S. Pub. No. 2004/0222936 A1), “MULTI-BAND DIPOLE ANTENNA”, filed Jul. 20, 2003, published Nov. 11, 2004 discloses a multi-band dipole antenna element that consists of metallic plate or metal film formed on an insulating substrate that comprises slots in the metal with an “L-shaped” conductor material located within the slot that causes the dipole to be resonant at certain select frequency bands.
Wu, U.S. Pat. No. 6,545,645 B1, “COMPACT FREQUENCY SELECTIVE REFLECTIVE ANTENNA”, filed Sep. 10, 1999, issued Apr. 8, 2003 disclose the use of optical interference between reflective antenna surfaces to selective specific frequencies within a range of electromagnetic frequencies.
Kaminski and Kolsrud, U.S. Pat. No. 6,147,572, “FILTER INCLUDING A MICROSTRIP ANTENNA AND A FREQUENCY SELECTIVE SURFACE”, filed Jul. 15, 1998, issued Nov. 14, 2000 discloses the use of a micro-strip antenna element co-located within a cavity to form a device that selective filters frequencies from a range of electromagnetic frequencies.
Ho et al., U.S. Pat. No. 5,917,458, “FREQUENCY SELECTIVE SURFACE INTEGRATED ANTENNA SYSTEM”, filed Sep. 8, 1995, issued Jun. 29, 1999 discloses a frequency selective dipole antenna that has frequency selectivity by virtue of being integrated upon the substrate that is designed to operate as a frequency selective substrate.
MacDonald, U.S. Pat. No. 5,608,413, “FREQUENCY-SELECTIVE ANTENNA WITH DIFFERENT POLARIZATIONS”, filed Jun. 7, 1995, issued Mar. 4, 1997 discloses an antenna formed using co-located slot and patch radiators to mildly select frequencies and alter the polarization of radiation emissions.
Stephens, U.S. Pat. No. 4,513,293, “FREQUENCY SELECTIVE ANTENNA”, filed Nov. 12, 1981, issued Apr. 23, 1985, discloses an antenna comprising a plurality of parabolic sections in the form of concentric rings or segments that allow the antenna uses mechanically means to select specific frequencies within a range of electromagnetic frequencies.
2. Definition of Terms    The term “active component” is herein understood to refer to its conventional definition as an element of an electrical circuit that that does require electrical power to operate and is capable of producing power gain.    The term “amorphous material” is herein understood to mean a material that does not comprise a periodic lattice of atomic elements, or lacks mid-range (over distances of 10's of nanometers) to long-range crystalline order (over distances of 100's of nanometers).    The terms “chemical complexity”, “compositional complexity”, “chemically complex”, or “compositionally complex” are herein understood to refer to a material, such as a metal or superalloy, compound semiconductor, or ceramic that consists of three (3) or more elements from the periodic table.    The terms “discrete assembly” or “discretely assembled” is herein understood to mean the serial construction of an embodiment through the assembly of a plurality of pre-fabricated components that individually comprise a discrete element of the final assembly.    The term “emf” is herein understood to mean its conventional definition as being an electromotive force.    The term “integrated circuit” is herein understood to mean a semiconductor chip into which at least one transistor element has been embedded.    The term “LCD” is herein understood to mean a method that uses liquid precursor solutions to fabricate materials of arbitrary compositional or chemical complexity as an amorphous laminate or free-standing body or as a crystalline laminate or free-standing body that has atomic-scale chemical uniformity and a microstructure that is controllable down to nanoscale dimensions.    The term “liquid precursor solution” is herein understood to mean a solution of hydrocarbon molecules that also contains soluble metalorganic compounds that may or may not be organic acid salts of the hydrocarbon molecules into which they are dissolved.    The term “meta-material” is herein understood to define a composite dielectric material that consists of a low-loss host material having a dielectric permittivity in the range of 1.5≦∈R≦5 with at least one dielectric inclusion embedded within that has a dielectric permittivity of ∈R≧10 or a dielectric permeability μR≠1 that produces an “effective dielectric constant” that is different from either the dielectric host or the dielectric inclusion.    The term “microstructure” is herein understood to define the elemental composition and physical size of crystalline grains forming a material substance.    The term “MISFET” is herein understood to mean its conventional definition by referencing a metal-insulator-semiconductor field effect transistor.    The term “mismatched materials” is herein understood to define two materials that have dissimilar crystalline lattice structure, or lattice constants that differ by 5% or more, and/or thermal coefficients of expansion that differ by 10% or more.    The term “MOSFET” is herein understood to mean its conventional definition by referencing a metal-oxide-silicon field effect transistor.    The term “nanoscale” is herein understood to define physical dimensions measured in lengths ranging from 1 nanometer (nm) to 100's of nanometers (nm).    The term “passive component” is herein understood to refer to its conventional definition as an element of an electrical circuit that that does not require electrical power to operate and is not capable of producing power gain.    The term “standard operating temperatures” is herein understood to mean the range of temperatures between −40° C. and +125° C.    The terms “tight tolerance” or “critical tolerance” are herein understood to mean a performance value, such as a capacitance, inductance, or resistance that varies less than ±1% over standard operating temperatures.
In view of the above discussion, it would be beneficial to have methods to have antenna systems that reduce the cost, component count, power consumption and occupied volume in fixed wireless and mobile wireless systems by either using a single antenna element to selectively filter multiple bands. For the same purposes, it would also be beneficial to have a high radiation efficiency narrow band antenna that eliminates the need for additional filtering components in the RF front-end. It would also be beneficial to have a high radiation efficiency narrow band that can be actively tuned to vary its center frequency to mitigate the need for multiple radio systems in a globally portable wireless device.
It is an object of the present invention to provide a single antenna element that is strongly resonant over multiple selective frequency bands or all communications bands of interest for a particular device to eliminate the need for multiple antenna systems, thereby minimizing cost, component count, and occupied volume without compromising the mobile system's signal integrity.
It is a further object of the present invention to provide a single antenna element that has a sufficiently narrow conductance band (25 MHz to 60 MHz) to isolate uplink frequencies from the downlink frequencies in the same communications band, thereby eliminating the need to add filtering components, like acoustic-wave filters, to the RF front-end to minimize cost, component count and occupied volume.
It is yet another object of the present invention is to provide a narrow band (25 MHz to 60 MHz) antenna system that can actively retune the center frequency of a narrow conductive pass band to accommodate a plurality of communications frequency band tunings with a single antenna element.